4-1 dissolution reactions • 4-2 precipitation reactions...

1/15/2004 OFB Chapter 4 1

Chapter 4Types of Chemical Reactions

• 4-1 Dissolution Reactions• 4-2 Precipitation Reactions• 4-3 Acids and Bases and Their Reactions• 4-4 Oxidation-Reduction Reactions


1. Dissolution– Ionic Compounds in Water– Molecular Compounds in Water– Electrolytes and Non-Electrolytes– Solubilities (like dissolves like)– Predicting Dissolution Reactions

2. Precipitation Reactions– Ionic Equations and Net Ionic Equations– Predicting Precipitation Reactions

3. Acids and Bases– Arrhenius Acids and Bases Theory– Strong and Weak acid– Naming Acids– Weak Bases– Modifying the Arrhenius model– Acid-Base Titrations

4. Oxidation-Reduction Reactions (Redox) Reactions– Oxidizing and Reducing Agents– Oxidation Number– Types of Redox Reactions

» Combination and Decomposition» Oxygenation» Hydrogenation» Displacement Reactions» Disproportionation


Dissolution:

Solution:

Two (or more) substances spread out, or disperse, into each other at the level of individual atoms, molecules, or ions.

Solvent:

Solute:

In principle, the solute and solvent can be any combination of solid (s), liquid (l), and gaseous (g) phases.


Ionic Compounds in Water:

All ionic compounds are solids in the range of temperature in which water is a liquid. They have rigid lattices in which strong forces (ionic bonds) pin the constituent ions in place.

The high melting points of ionic compounds indicate that a good deal of energy must be supplied to destroy the lattice and produce a liquid (molten) form in which the ions move more freely.

Aquation:


Ionic Compounds in Water:

Solute is said to dissociate into ions or to ionize upon dissociation.


Molecular Compounds in Water:

Molecular substances (covalent) contain no ions to which water molecules can adhere, but their molecules are often polar.

Example: members of the class of carbohydrates known as sugars have the general formula, Cm(H2O)n.

Typical sugars include sucrose, C12H22O11 (table sugar); fructose, C6H12O6(fruit sugar); and ribose, C5H10O5 (a subunit in the biomolecules ribonucleic acids).

C6H12O6(s) → C6H12O6(aq)


Solubilities:

Miscible:

Solubility: The largest amount that can dissolve in a given amount of a solvent at a particular temperature.


• Pairs of liquids that mix in any proportion are termed miscible. Liquids that do not mix are termed immiscible

• "Like dissolves like"– in other words, substances with similar

intermolecular attractive forces tend to be soluble in one another


“like dissolves like” conceptCHO

OHH

HOH

OHH

OHH

CH2OH

O

H

HO

H

HO

H

OH

OHHH

OH

OH

HO

OHHO

HO

Ofructose

O

OHHO

OHHO

HO

glucose

NH2

O

OH

alanine

HOethanol

OHH

water

OH

OH

HO

O

HO

O

OH

OH

HO

HOO

sucrose

= =

1/15/2004 OFB Chapter 4 10

“like dissolves like” concept

HOoctanol

octane

benzene

isobutane

cyclohexane

ClCl

Cl

Cl

carbon tetrachloride

Non-Polar

1/15/2004 OFB Chapter 4 11

Electrolytes and Non-Electrolytes:

Electrolytes:

Non-Electrolytes:

Strong electrolytes:

1/15/2004 OFB Chapter 4 12

Predicting Dissolution Reactions

1/15/2004 OFB Chapter 4 13

Solubilities:

Exercise 4-1:

Predict whether the following substances are soluble in water:

(a) calcium carbonate (CaCO3)

(b) mercury(II) sulfide (HgS)

(c) isopropanol (C3H7OH)

1/15/2004 OFB Chapter 4 14






1/15/2004 OFB Chapter 4 15

CHEM1310 McKelvy LectureCHEM1310 McKelvy LectureCHEM1310 McKelvy Lecture

1/15/2004 OFB Chapter 4 16

Solubility Rules

1. All common sodium, potassium and ammonium salts are soluble in water

2. The chloride and iodide salts of all common metals, except silver, lead and mercury (I), are soluble in water. Lead chloride is soluble in hot water.

3. The sulfates of all metals, excepts lead, mercury (I), barium, strontium, and calcium are soluble in water.

4. The carbonates of all metals, except those of Group 1A and ammonium carbonate, are insoluble in water

5. Most metal hydroxides are insoluble in water. However, the hydroxides of group 1A are soluble and those of Group IIA are moderately soluble.

1/15/2004 OFB Chapter 4 17

Precipitation Reactions:

A new solid phase is usually dense enough to sink to the bottom of a liquid solution.

Whenever the concentration of a substance in solution exceeds its solubility, a new phase starts to separate.

Solids usually precipitate (“fall down”) from their solution.

1/15/2004 OFB Chapter 4 18

Ionic Equations and Net Ionic Equations:

BaCl2(aq) + K2SO4(aq) → BaSO4(s) + 2 KCl(aq)

Ionic equation

Spectator ions

Net ionic equation

1/15/2004 OFB Chapter 4 19

Exercise 4-2:

Write a net ionic equation to represent the formation of the precipitate observed when aqueous solutions of CaCl2 and NaF are mixed. Identify the spectator ions in this process.

1/15/2004 OFB Chapter 4 20






1/15/2004 OFB Chapter 4 21

Acids and Bases and Their Reactions

Acid Base Theory1. Arrhenius Acids and Bases (Chapter 4)

• Acids are H+ donors• Bases are OH- donors

2. Arrhenius Broadened Definition (Chapter 4)• Acids increase H+ concentration or [H+] increases• Bases increase OH- concentration or [OH-] increases

3. Brønsted Acids and Bases (Chapter 8)• Acids donate H+

• Bases accept H+

4. Lewis Acids and Bases (Chapter 8)• Acids are electron pair acceptors• Bases are electron pair donors

1/15/2004 OFB Chapter 4 22

Acids and Bases and Their Reactions:

CR O

H

O

1/15/2004 OFB Chapter 4 23

Arrhenius Acids and Bases:

An Arrhenius acid is a substance that, when dissolved in water, delivers hydrogen ions (H+(aq) ions) to the solution; it is a hydrogen-ion donor.An Arrhenius base is a substance that, when dissolved in water, delivers hydroxide ions (OH-(aq) ions) to the solution; it is a hydroxide-ion donor.

Water is simultaneously and equally both an acid and a base:

1/15/2004 OFB Chapter 4 24


Strong acids:

Strong bases:

1/15/2004 OFB Chapter 4 25


Neutralization reaction:

HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)

1/15/2004 OFB Chapter 4 26

Weak Acids

CH3COOH(aq) → CH3COO-(aq) + H+(aq) (dissociation of acetic acid)

CH3COOH(aq) + NaOH(aq) → NaCH3COO(aq) + H2O(l) (overall equation)

1/15/2004 OFB Chapter 4 27

Naming Acids

Binary acids:

•HCl as covalent compound is hydrogen chloride

•HCl as a binary acid is hydrochloric Acid

Oxoacids:

• SO4-2 or Sulfate ion

• H2SO4 becomes Sulfuric Acid

Organic acids:

• HCOO- or Formate ion becomes Formic Acid

(R=H)

Oxoacids:

• SO3-2 or Sulfite ion

• H2SO3 becomes Sulfurous Acid

CR O

H

O

1/15/2004 OFB Chapter 4 28

An Arrhenius base is a substance that, when dissolved in water, increases the concentration of hydroxide ions over what is present in the pure solvent.

Modifying the Arrhenius Model

An Arrhenius acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions over what is present in the pure solvent.

1/15/2004 OFB Chapter 4 29

Acid-Base Titrations

A controlled addition of measured volumes of a solution of known concentration to a second solution of unknown concentration under conditions in which the solutes react cleanly (without side reactions), completely, and rapidly.

Titration:

A titration is complete when the second solute is used up.

Completion is signaled by a change in some physical property, such as the color of the reacting mixture or the color of an indicator that has been added to it.

1/15/2004 OFB Chapter 4 30

[NaOH]

“X”

Indicator phenolphthalein

1/15/2004 OFB Chapter 4 31

Exercise 4-6

Compute the molarity of a solution of sodium hydroxide if 25.64 mL of solution must be added to a solution containing 0.5333 g of KHC8H4O4 (potassium hydrogen phthalate abbreviated KHP) to reach the phenolphthalein end-point.

1/15/2004 OFB Chapter 4 32

Exercise 4-4

Give the name for the acid H2SeO3. Write the overall, ionic, and net ionic equations for the complete neutralization of H2SeO3 by sodium hydroxide.

Start with something we know:

Selenium (Se) is in Group VI with Sulfur (S)

H2SO4 is Sulfuric Acid and H2SO3 is Sulfurous Acid

1/15/2004 OFB Chapter 4 33

Acids and Bases and Their Reactions

Acid Base Theory1. Arrhenius Acids and Bases (Chapter 4)

• Acids are H+ donors• Bases are OH- donors

2. Arrhenius Broadened Definition (Chapter 4)• Acids increase H+ concentration or [H+] increases• Bases increase OH- concentration or [OH-] increases

3. Brønsted Acids and Bases (Chapter 8)• Acids donate H+

• Bases accept H+

4. Lewis Acids and Bases (Chapter 8)• Acids are electron pair acceptors• Bases are electron pair donors

1/15/2004 OFB Chapter 4 34






1/15/2004 OFB Chapter 4 35

Oxidation-Reduction or Redox Reactions

• Definitions– Oxidation and Reduction– Oxidation Numbers

• Types of Redox Reactions– Combination– Decomposition– Oxygenation– Hydrogenation– Displacement– Disproportionation

1/15/2004 OFB Chapter 4 36

Oxidation-Reduction Reactions

Redox: an extensive and important class of reactions that is characterized by the transfer of electrons.

2 Mg(s) + O2(g) → 2 MgO(s)

Magnesium is oxidized: it gives up electrons as the charge on its atoms increases from zero to +2.Oxygen is reduced: it gains electrons as the charge on its atoms decreases from zero to -2 (i.e., becomes more negative).

1/15/2004 OFB Chapter 4 37

Oxidation Numbers (also called oxidation states) are determined for the atoms in covalently bonded compounds by applying the following set of simple rules:

1. The oxidation number of the atoms in a neutral molecule must all up to zero; those in an ion must add up to the charge on the ion.

2. Alkali metal (Group I) atoms have oxidation number +1, and alkaline earth (Group II) atoms have oxidation number +2 in their compounds; atoms of Group III elements usually have oxidation number +3 in their compounds.

3. Fluorine always has an oxidation number of -1 in its compounds. The other halogens have oxidation number -1 in their compounds, except in compounds with oxygen and with other halogens, in which they can have positive oxidation numbers.

1/15/2004 OFB Chapter 4 38

Oxidation Numbers (also called oxidation states) are determined for the atoms in covalently bonded compounds by applying the following set of simple rules:

4. Hydrogen is assigned an oxidation number of +1 in its compounds, except in metal hydrides such as LiH, in which rule 2 take precedence and hydrogen has an oxidation number of -1.

5. Oxygen is assigned an oxidation number of -2 in compounds. There are two exceptions: in compounds with fluorine, rule 3 takes precedence, and in compounds that contain O—O bonds, rules 2 and 4 take precedence. Thus, the oxidation number of oxygen in OF2 is +2; in peroxides (e.g., H2O2 and Na2O2), its oxidation number is -1, and in superoxides(e.g., KO2), its oxidation number is -½.

1/15/2004 OFB Chapter 4 39

What is the Nitrogen Atom Oxidation State?

NO2

NO2+1

NO3-1

HONO2NO2

-1

Hint consider HO as HO–1

1/15/2004 OFB Chapter 4 40

Assign Oxidation Numbers to each of the following

Ethane C2H6

Acetic Acid C2H4O2

Ammonium Nitrate NH4NO3

Potassium superoxide KO2

Hint: NH4+1 NO3

-1

1/15/2004 OFB Chapter 4 41

an atom is reduced (gains electrons) if its oxidation number decreases.

An atom is oxidized (loses electrons) if its oxidation number increases in a chemical reaction;

We can now state the following definition

1/15/2004 OFB Chapter 4 42

Gains ElectronsDecreaseSubstance Reduced

Loses ElectronsIncreaseSubstance Oxidized

Supplies ElectronsIncrease

Reducing Agent, does the reducing

Picks Up electronsDecrease

Oxidizing Agent, does the oxidizing

Gain of ElectronsDecreaseReduction

Loss of ElectronsIncreaseOxidation

Electron Change

Oxidation Number ChangeTerm

1/15/2004 OFB Chapter 4 43

Oxidation-Reduction reactions

O2 H2 H2O

Cl2 Na NaCl

Gains ElectronsDecreaseSubstance Reduced

Loses ElectronsIncreaseSubstance Oxidized

Supplies ElectronsIncreaseReducing Agent, does the reducing

Picks Up electronsDecreaseOxidizing Agent, does the oxidizing

Electron ChangeOxidation Number ChangeTerm

H+ Mg Mg++ + H2

1/15/2004 OFB Chapter 4 44

Oxidation-Reduction or Redox Reactions

• Definitions– Oxidation and Reduction– Oxidation Numbers

• Types of Redox Reactions– Combination– Decomposition– Oxygenation– Hydrogenation– Displacement– Disproportionation

1/15/2004 OFB Chapter 4 45

Types of Redox ReactionsRedox Combination and Decomposition Reactions

P4(s) + 6 Cl2(g) → 4 PCl3(l)

P4(s) + 10 Cl2(g) → 4 PCl5(l)

2 HgO (s) → 2 Hg(l) + O2(g)

2 Hg2O(s) → 4 Hg(l) + O2(g)

2 H2O2 (l) → 2 H2O(l) + O2(g)

1/15/2004 OFB Chapter 4 46

Types of Redox ReactionsOxygenation and Hydrogenation

4 Li (s) + O2(g) → 2 Li2O(s)

2 ZnS(s) + 3 O2(g) → 2 ZnO(s) + 2 SO2(g)

2 Na(l) + H2(g) → 2 NaH(s)

Fe2O3(s) + 3 H2(g) → 2 Fe(s) + 3 H2O(g)

1/15/2004 OFB Chapter 4 47

Types of Redox ReactionsDisplacement Reactions

2 AgNO3(aq) + Cu(s) → Cu(NO3)2(aq) + 2 Ag(s) (overall equation)

2 Ag+(aq) + Cu(s) → Cu2+(aq) + 2 Ag(s) (net ionic equation)

Cl2(g) + 2 KI(aq) → I2(s) + 2 KCl(aq) (overall equation)

Cl2(g) + 2 I-(aq) → I2(s) + 2 Cl-(aq) (net ionic equation)

Referring to the information (page 178) of Ability to Replace

1/15/2004 OFB Chapter 4 48

Types of Redox ReactionsDisproportionation

2 H2O2 (l) → 2 H2O(l) + O2(g)

2 Cu+(aq) → Cu2+(aq) + Cu(s) (net ionic equation)

1/15/2004 OFB Chapter 4 49






1/15/2004 OFB Chapter 4 50

Chapter 4: Types of Chemical ReactionsChapter 4: Types of Chemical Reactions

Acknowledgement: Many of the slide used in this Chapter were originally prepared by Dr. George McKelvy

Examples and Exercises:

All (4-1 to 4-12)

Homework:

1, 6, 12, 50, 54, 55, 59, 71

4-1 dissolution reactions • 4-2 precipitation reactions...

Documents